Patent GB-190711288-A (GB)
Title: Improvements in or relating to Alternate Current Motors.
Inventor: FYNN VALERE ALFRED
Filed: 1907-05-14
Granted: 1908-05-14
Abstract: 11,288. Fynn, V. A. May 14. Motors, alternating-current. -In a single-phase commutator motor of the induction or inductionconduction type, in which the 'field' winding is at least partly disposed on the rotor, and in which at least two rotor circuits the axes of which do not coincide are connected in series relation, the phase of the rotor field-exciting current is so chosen as to yield at a given speed a negative torque in conjunction with the inducing or transformer field for the purpose of reducing or limiting the no-load or light-load speed of the motor, thus destroying the series characteristic of the machine with decreasing load. The motors may be used as generators or brakes, for example in driving lifts. In one modification, Fig. 3, the 'armature' brushes a are connected to the primary winding of a transformer T, having a large magnetizing-current, the secondary winding of the transformer being closed on the 'field' brushes b. The main torque of the motor is due to the interaction of the current i<2> flowing through the brushes a and the field in the axis of the brushes b, while an auxiliary torque may be produced between the ' field' current i<3> and the transformer field due to the stator winding S, depending upon the phase relation of the current i<2> and the electromotive force induced by the trans - former field across the brushes a. The auxiliary torque is positive or negative according as the current i' lags behind or leads that electromotive force, and is zero when they are cophasal. This phase difference may be adjusted and the motor regulated by varying the transformation ratio of the transformer T by the use of movable contacts Ka, Kb, and by suitably choosing the effective number of turns of those windings acting as field windings. The motor shown in Fig. 3 may be given a shunt characteristic after starting by switching out or short-circuiting the transformer T by means of a switch M, Fig. 5, operated either by hand or by a centrifugal or an electro-magnetic device, the transformer T being also used to compensate the motor by connecting its primary winding to a part of the stator winding S, or other suitable source ; or the compensating electromotive force may be derived from an auxiliary winding on the stator. The brushes a, b may be disposed along axes not at right-angles, and the axis of the brushes a may not coincide with that of the winding S. Another brush arrangement is shown in Fig. 7, the switch E being closed when the motor is to operate as a shunt motor ; or that arrangement may be duplicated by the use of two transformers T, which may have a common core. The motor may have two independent rotor windings, Fig. 9, and an auto-transformer T may be used. According to another modification, the field winding may be partly disposed on the stator as at F, Fig. 10, and the speed of the motor is limited by connecting the winding F so that it opposes the field winding disposed on the rotor ; the transformer T may then be dispensed with if the rotor is provided with two separate windings in some such manner as is shown in Fig. 9. Energy may be conveyed into the rotor partly by induction from the winding S and partly by conduction from the mains, for example by connecting the brushes a to the mains through a shunt transformer. When the transformer employed for the purposes of the invention is embodied in the motor itself, it must be placed so as not to be in effective inductive relation to either stator or rotor, or its flux should induce electromotive forces in the windings which cancel out at the terminals of the windings or of the motor. The motors may have any number of poles.